The word corrosion comes from the Latin "corrodo" - "gnaw" (Late Latin "corrosio" means "erosion"). Corrosion is caused by a chemical reaction of a metal with environmental substances that occurs at the interface between the metal and the medium. Most often this is the oxidation of the metal, for example, with atmospheric oxygen or acids contained in solutions with which the metal is in contact. Especially susceptible to this are metals located in a series of voltages (a series of activity) to the left of hydrogen, including iron.

Chemical corrosion t Fe + 3 SO O 2 Fe 2 (SO 4) t Fe + 3 Cl 2 2 FeCl t Zn + O 2 2 ZnO Corrosion occurs in a non-conductive environment. For example, the interaction of a metal with dry gases or liquids - non-electrolytes (gasoline, kerosene, etc.)

Many metals (for example, aluminum) are covered with a dense oxide film during corrosion, which prevents oxidants from penetrating into deeper layers and therefore protects the metal from corrosion. When this film is removed, the metal begins to interact with moisture and oxygen in the air.

Electrochemical corrosion Corrosion occurs in a conductive medium (in an electrolyte) with the appearance of an electric current inside the system. Metals are not homogeneous and contain various impurities. When they come into contact with electrolytes, some parts of the surface act as anodes, others as cathodes.

Let us consider the destruction of an iron sample in the presence of a tin impurity. 1. In an acidic environment: On iron, as a more active metal, in contact with an electrolyte, the processes of oxidation (dissolution) of the metal and the transition of its cations into the electrolyte occur: Fe 0 - 2 e = Fe 2+ (anode) On the cathode (tin) reduction of hydrogen cations: 2H + + 2e H 2 0 Rust is not formed, because iron ions (Fe 2+) go into solution

2. In an alkaline or neutral medium: Fe 0 - 2e Fe 2+ (at the anode) OH 2 O + 4e 4OH - (at the cathode) ________________________________________________________ Fe OH - Fe (OH) 2 4 Fe (OH) 2 + O 2 + 2H 2 O = 4 Fe (OH) 3 (Rust)

1. Grinding the surfaces of the product so that moisture does not linger on them. 2. The use of alloyed alloys containing special additives: chromium, nickel, which at high temperatures on the metal surface form a stable oxide layer (for example Cr 2 O 3). forks, spoons), machine parts, tools.

3. Application of protective coatings Non-metallic - non-oxidizing oils, special varnishes, paints, enamels. True, they are short-lived, but cheap. Chemical - artificially created surface films: oxide, nitride, silicide, polymer, etc. For example, all small arms and parts of many precision instruments are blued - this is the process of obtaining the thinnest film of iron oxides on the surface of a steel product.

Metallic is a coating with other metals, on the surface of which, under the action of oxidants, stable protective films are formed. Chromium plating, nickel - nickel plating, zinc - zinc plating, etc. A chemically passive metal - gold, silver, copper - can also serve as a coating.

4. Electrochemical methods of protection 4. Electrochemical methods of protection * Protective (anodic) - a piece of more active metal (protector) is attached to the protected metal structure, which serves as an anode and is destroyed in the presence of an electrolyte. Magnesium, aluminum, zinc are used as a protector in the protection of ship hulls, pipelines, cables and other steel products. * Cathodic - the metal structure is connected to the cathode of an external current source, which excludes the possibility of its anodic destruction.

Introduction of substances - corrosion inhibitors. Examples of the use of modern inhibitors: hydrochloric acid during transportation and storage is perfectly "tamed" by butylamine derivatives, and sulfuric acid by nitric acid; volatile diethylamine is injected into various containers. Inhibitors act only on metal, making it passive in relation to the environment. More than 5 thousand corrosion inhibitors are known to science. Removal of oxygen dissolved in water (deaeration). This process is used in the preparation of water entering boiler plants. 5. Special treatment of electrolyte or other environment in which the protective metal structure is located

To use the preview of presentations, create yourself a Google account (account) and log into it: https://accounts.google.com

Slide captions:

Metals have an enemy, which leads to huge irretrievable losses of metals, annually about 10% of the produced iron is completely destroyed. According to the Institute of Physical Chemistry of the Russian Academy of Sciences, every sixth blast furnace in Russia is wasted - all smelted metal turns into rust. This enemy is corrosion.

The problem of protecting metals from corrosion arose almost at the very beginning of their use. People tried to protect metals from the weather by using grease, oils, and later by coating with other metals and, above all, with low-melting tin (tin plating). In the writings of the ancient Greek historian Herodotus (5th century BC), there is already a mention of the use of tin to protect iron from corrosion.

In III BC, a lighthouse in the form of a huge statue of Helios was built on the island of Rhodes. The Colossus of Rhodes was considered one of the seven wonders of the world, but lasted only 66 years and collapsed during an earthquake. At the Colossus of Rhodes, a bronze shell was mounted on an iron frame. Under the influence of the humid, salty Mediterranean air, the iron frame collapsed.

In the 20s of the twentieth century. the luxury yacht “Call of the Sea” was built by the order of one millionaire. Even before entering the open sea, the yacht was completely out of order. Contact corrosion was the cause. The bottom of the yacht was sheathed with a copper-nickel alloy, and the rudder frame, keel and other parts were made of steel. When the yacht was launched. A giant galvanic cell was formed, consisting of a bottom cathode, a steel anode and an electrolyte - sea water. As a result, the ship sank without making a single voyage.

What is the symbol of Paris? -The Eiffel Tower. It is incurably ill, rusts and collapses, and only constant chemotherapy helps to fight this deadly disease: it was painted 18 times, which makes its weight of 9000 tons each time increasing by 70 tons.

Corrosion is the destruction of metals and alloys under the influence of the environment. The word corrosion comes from the Latin corrodere, which means to corrode.

Types of corrosion

Chemical corrosion Chemical corrosion is the interaction of metals with dry gases and liquids - non-electrolytes. Turbines, furnace fittings and parts of internal combustion engines are exposed to this type of corrosion.

Electrochemical corrosion Electrochemical corrosion is all cases of corrosion in the presence of water and liquids - electrolytes.

The essence of corrosion. Corrosion consists of two processes: chemical - this is the return of electrons and electrical - this is the transfer of electrons.

Regularities of corrosion: 1. If two different metals are connected, then only the more active undergoes corrosion, and until it is completely destroyed, the less active is protected.

Regularities of corrosion: 2. The rate of corrosion is the greater, the further apart in the series of stresses the connected metals are located.

Corrosion chemistry.

Corrosion protection methods. One of the most common ways to protect metals from corrosion is to apply protective films to their surface: varnish, paint, enamel.

A widespread method of protecting metals from corrosion is to coat them with a layer of other metals. The coating metals themselves corrode at a low rate, since they are covered with a dense oxide film. Plating with zinc, nickel, chromium, etc.

Plating with other metals.

In everyday life, a person most often encounters iron coatings with zinc and tin. Zinc-coated sheet metal is called galvanized iron, and tin-coated sheet metal is called tinplate. The first goes to the roofs of houses in large quantities, and cans are made from the second.

Corrosion protection methods. Creation of alloys with anti-corrosion properties. For this, up to 12% of chromium, nickel, cobalt or copper is added to the base metal.

Corrosion protection methods. Changes in the composition of the environment. Inhibitors are added to slow down corrosion. These are substances that slow down the rate of reaction.

Corrosion protection methods. The use of inhibitors is one of the most effective ways to combat metal corrosion in various aggressive environments (atmospheric, sea water, coolants and saline solutions, under oxidizing conditions, etc.). Inhibitors are substances that, in small quantities, can slow down or stop chemical processes. The name of the inhibitor comes from lat. inhibere, which means to restrain, to stop. It is known that Damascus craftsmen used solutions of sulfuric acid with the addition of brewer's yeast, flour, and starch to remove scale and rust. These impurities were among the first inhibitors. They did not allow the acid to attack the weapon metal, as a result of which only scale and rust dissolved.

Electrical protection. 1. Protective protection. Rivets or plates of a more active metal are attached to the main structure, which are destroyed. Such protection is used in underwater and underground structures.

Electrical protection. 2. Passing an electric current in the opposite direction to that which occurs during the corrosion process.

Thank you for the attention!

Description of the presentation PRESENTATION on the topic “Corrosion of metals on slides

Corrosion of metals Introduction Chemical corrosion Electrochemical corrosion The essence of corrosion processes Methods of protection against corrosion Atmospheric corrosion of steel Inhibitors of corrosion of metals

Introduction The word corrosion comes from the Latin corrodere, which means to corrode. Although corrosion is most commonly associated with metals, stones, plastics and other plastics, and wood are also affected. For example, at the present time we are witnessing a great concern of wide layers of people in connection with the fact that monuments (buildings and sculptures) made of limestone or marble are catastrophically suffering from acid rains. Thus, corrosion is a spontaneous process of destruction of materials and products from them under the chemical influence of the environment. Processes of physical destruction are not classified as corrosion, although they often cause no less harm to cultural monuments. They are called abrasion, wear, erosion.

Metals are one of the foundations of civilization on planet Earth. Among them, iron stands out as a structural material. The volume of industrial production of iron is about 20 times greater than the volume of production of all other metals combined. The widespread introduction of iron in industrial construction and transport took place at the turn of the XVIII. ... ... XIX centuries. At this time, the first cast-iron bridge appeared, the first ship was launched, the hull of which was made of steel, and the first railways were created. However, the beginning of the practical use of iron by humans dates back to the 9th century. BC NS. It was during this period that mankind passed from the Bronze Age to the Iron Age. Nevertheless, history indicates that iron products were known in the Hittite kingdom (the state of Asia Minor), and its heyday is attributed to the XIV. ... ... XIII centuries BC NS.

In nature, although very rarely, native iron is found. Its origin is considered meteorite, that is, cosmic, and not terrestrial. Therefore, the first items made of iron (they were made from nuggets) were valued very highly - much higher than from silver and even gold.

Despite the widespread introduction of polymeric materials, glass, ceramics into our modern life, iron and its alloys continue to be the main structural material. We meet iron products at every step in everyday life and we know how much trouble is caused by its rusting and rust itself. Only the corrosion of iron and its alloys is called rusting. Other metals corrode but do not rust. Although almost all metals corrode, in everyday life a person most often encounters iron corrosion.

Chemical corrosion Chemical corrosion of steel is caused by dry gases and liquids that do not have the character of electrolytes, for example, organic compounds or solutions of inorganic substances in organic solvents. Chemical corrosion is not accompanied by an electric current. It is based on the reaction between a metal and an aggressive reagent. This type of corrosion occurs mainly evenly over the entire surface of the metal. In this regard, chemical corrosion is less dangerous than electrochemical.

Corrosion products can form a dense protective layer on the metal surface, which inhibits its further development, or a porous layer that does not protect the surface from the destructive effects of the environment. In this case, the corrosion process continues until the material is completely destroyed or for a period of time until an aggressive environment acts. The most common in practice is gas corrosion of steel caused by exposure to O 2, SO 2, H 2 S, CI, HC 1, NO 3, CO 2, CO and H 2.

Electrochemical corrosion Electrochemical corrosion occurs when metals interact with liquid electrolytes, mainly solutions of acids, bases and salts. The mechanism of the corrosion process depends on the structure of the metal, as well as on the type of electrolyte. Steel, like any metal, has a crystalline structure, in which the atoms are arranged in the appropriate order, forming a characteristic spatial lattice. Iron crystals have a structure that significantly differs from the ideal scheme, since there are voids not occupied by metal atoms, cracks, and inclusions of impurities to gases.

Metals have good electrical conductivity, which is due to the presence of free electrons, the movement of which creates an electric current. The number of free electrons corresponds to the equivalent number of ion-atoms, ie, atoms that have lost one or more electrons. If a potential difference arises at the ends of the metal rod, the electrons move from the pole with the highest potential to the opposite pole. Metals with electronic conductivity are type I conductors, and electrolytes that have ionic conductivity are type II conductors.

Depending on the type and content of salts dissolved in water, not only normal potentials, but even the position of the metal in the series of potentials are subject to change.

The essence of corrosion processes. Corrosion of metals is most often reduced to their oxidation and transformation into oxides. In particular, iron corrosion can be described by the simplified equation 4 Fe + 3 O 2 + 2 H 2 O = 2 Fe 2 O 3 H 2 O Hydrated iron oxide Fe 2 O 3 H 2 O and is what people call rust ... It is a light brown loose powder. During corrosion, many metals are covered with a dense oxide film that is well bonded to the metals, which does not allow oxygen in the air and water to penetrate into deeper layers and therefore protects the metal from further oxidation. For example, aluminum is a very active metal and theoretically should interact with water in accordance with the equation 2 Al + 3 H 2 O = Al 2 O 3 + 3 H

It is difficult and sometimes impossible to strictly separate chemical and electrochemical corrosion. The fact is that electrochemical corrosion is often associated with the presence of random impurities or specially introduced alloying additives in the metal.

Corrosion protection methods. The problem of protecting metals from corrosion arose almost at the very beginning of their use. People tried to protect metals from the weather with the help of grease, oils, and later with coating with other metals and, above all, low-melting tin (tin plating). In the writings of the ancient Greek historian Herodotus (5th century BC), there is already a mention of the use of tin to protect iron from corrosion.

Cement coatings are used to protect cast iron and steel water pipes from corrosion. Since the coefficients of thermal expansion of Portland cement and steel are close, and the cost of cement is low, it is widely used for these purposes. The disadvantage of Portland cement coatings is the same as that of enamel coatings - high sensitivity to mechanical shock.

A widespread method of protecting metals from corrosion is to coat them with a layer of other metals. The covering metals themselves corrode at a low rate, since they are covered with a dense oxide film. The coating layer is applied by various methods: short-term immersion in a bath with molten metal (hot coating), electrodeposition from aqueous solutions of electrolytes (galvanic coating), spraying (metallization), processing with powders at elevated temperatures in a special drum (diffusion coating), using a gas-phase reaction , for example 3 Cr. Cl 2 + 2 Fe - → 2 Fe. Cl 3 + 3 Cr (in an alloy with Fe).

There are other methods of applying metal coatings, for example, a type of diffusion method for protecting metals is immersion of products in a molten calcium chloride Ca. Cl 2, in which the deposited metals are dissolved.

Atmospheric corrosion of steel The most common type of steel corrosion in practice is the formation of rust under the influence of atmospheric influences (most often oxygen and humidity). In dry atmospheric air, steel practically does not corrode. Atmospheric corrosion is electrochemical in nature, and the electrolyte is a layer of moisture on the metal surface.

Corrosion processes under atmospheric conditions are similar to the corrosion of steel in water containing oxygen. The corrosion products covering the metal are hydrated iron oxides with a composition determined by the formula The rate of atmospheric corrosion depends on the moisture content in the air. An increase in the relative humidity of the air up to 70 -75% leads to relatively small losses of steel. At humidity exceeding these values, an intensive acceleration of corrosion processes is observed. Air pollution with aggressive products such as CO 2, SO 2, CI 2, H 2 S, smoke and soot intensifies corrosion. Steel that has been exposed to an industrial atmosphere for several years has significantly higher losses than steel in rural areas.

Inhibitors The use of inhibitors is one of the effective ways to combat metal corrosion in various aggressive environments (atmospheric, sea water, coolants and saline solutions, under oxidizing conditions, etc.). Inhibitors are substances that, in small quantities, can slow down or stop chemical processes. The name of the inhibitor comes from lat. inhibere, which means to restrain, to stop. Inhibitors interact with intermediate reaction products or with active sites on which chemical transformations take place. They are very specific to each group of chemical reactions. Metal corrosion is just one type of chemical reaction that is susceptible to inhibitors. According to modern concepts, the protective effect of inhibitors is associated with their adsorption on the surface of metals and the inhibition of anodic and cathodic processes.

The first inhibitors were found by chance, empirically, and often became clan secrets. It is known that Damascus craftsmen used solutions of sulfuric acid with the addition of brewer's yeast, flour, and starch to remove scale and rust. These impurities were among the first inhibitors. They did not allow the acid to attack the weapon metal, as a result of which only scale and rust dissolved.

According to 1980 data, the number of corrosion inhibitors known to science has exceeded 5 thousand. It is believed that 1 ton of inhibitor saves about 5000 rubles in the national economy. Corrosion control work is of the most important national economic importance. This is a very fertile area for the application of strength and ability.

Slide 2

Slide 3

Slide 4

Slide 5

Slide 6

Target

Investigate the effect of environmental factors on the degree of metal rusting. Hypothesis If iron is placed in an alkaline medium, the corrosion rate will decrease.

Slide 7

Tasks

1. To study the essence of corrosion, its types and methods of corrosion protection. 2. Investigate the dependence of the corrosion rate on the presence of oxygen. 3. Investigate the effect of electrolytes on the corrosion process. 4. Investigate the effect of inhibitors on the corrosion process.

Slide 8

Corrosion value

1. Causes serious environmental consequences: leakage of oil, gas, and other chemical products. 2. Unacceptable in many industries: aviation, chemical, oil and nuclear engineering. 3. Negatively affects the life and health of people.

Slide 9

Corrosion is a heterogeneous process that occurs at the metal-environment interface. As a result of corrosion, metals are oxidized and transform into stable compounds - oxides or salts, in the form of which they are found in nature.

Slide 10

In the case of chemical corrosion, the metal interacts directly with the oxidizing agent of the environment. As a result, the metal bond is destroyed, and the metal atoms are combined with the atoms and groups of atoms that make up the oxidizing agents. 2Fe0 + 3Cl20 → -2Fe + 3Cl3 3Fe + 2O2 → Fe3O4 Chemical corrosion.

Slide 11

Electrochemical corrosion

This type of corrosion occurs most often and is a process of interaction of metals and alloys with electrolytes, accompanied by the spontaneous emergence of galvanic pairs "cathode - anode". Iron anode (+) Copper cathode (-) Fe 0-2e = Fe2 + 2H ++ 2e = 2H0 → H20

Slide 12

Corrosive factors

1. Oxygen and moisture in the atmosphere 2. Carbon dioxide and sulfur dioxide in the atmosphere 3. Sea water 4. Ground water

Slide 13

Experiment # 1. The role of oxygen in the process of iron corrosion. In test tube No. 1-g. nail + water in half. In test tube No. 2-well. nail + water completely. In test tube No. 3-well. nails-water + oil.

Slide 14

Slide 15

Slide 16

Experiment # 2. The influence of electrolytes on the corrosion process. In glass No. 1-zh. nail + water. In glass No. 2-well. nail + sodium chloride solution. In glass No. 3-well. nail + copper + sodium chloride solution. In glass No. 4-well. nail + aluminum + sodium chloride solution.

Slide 17

Slide 18

Slide 19

Experiment # 3. The influence of inhibitors on the corrosion process. In test tube # 1 - well. nail + sodium hydroxide solution. In test tube # 2 - well. nail + sodium phosphate solution. In test tube No. 3 - well. nail + sodium dichromate solution.

Slide 20

Slide 21

Based on the research results, the following conclusions were made:

1. Corrosion of iron is sharply increased in the presence of oxygen. 2. Corrosion of iron increases sharply if it comes into contact with a less active metal, but corrosion slows down if iron comes into contact with a more active metal. 3. The corrosion rate depends on the composition of the environment washing the metal. Chloride ions enhance the corrosion of iron. 4. Corrosion of iron is weakened in the presence of hydroxide - ions, phosphate - ions and chromate - ions.